Process of coating paper with a gellable water-soluble cellulose derivative and pigment and gelling said coating



as-ntua-web PROCESS OF COATIN G PAPER WITH A GELLABLE WATER-SOLUBLE CELLULOSE DERIVATIVE AND PIGMENT AND GELLING SAID COATING George P. Gregory, Elsmere, Del., assignorto Hercules Powder Company, Wilmington, Del., a corporation of Delaware No Drawing. Application April 30, 1952, Serial No. 285,325

10 Claims. (Cl. 117-62) This invention relates to an improvement in coating paper with a coating composition or color to obtain a coated paper of the type having a base of cellulosic fibers and a printing surface consisting essentially of a film of contiguous pigment particles interspersed in binder. by means of which the pigment is retained on the base.

The paper coating colors as employed in the paper industry today consist essentially of a water solution of a nited States Patent binder such as starch or casein to which is addedfillers.

The adhesive filler mixture is appliedto paper in metered amounts and dried. The ratio of pigment to adhesive is regulated to provide sutficient bond between the coating and the paper base to prevent picking during the printing operation. The incorporation of the adhesive in the portions necessary to prevent picking results in certain disadvantages. For one thing, the optical properties of the coated sheet are adversely affected. Other disadvantages relate to factors affecting the lay of the ink and the ink drying rate, both of which properties are adversely affected by the high ratio of binder to pigment.

For some time it has been apparent that an adhesive which could be used in lesser amounts than casein or starch and still provide adequate strength against picking might conceivably result in improved optical properties and improved printing characteristics. Such a result has in fact been provided to a certain extent by the process of U. S. 2,502,783 to D. R. Erickson. This process comprises coating paper with a continuous viscous coating consisting of pigment dispersed in a solution of hydroxyethyl cellulose and aqueous sodium hydroxide, and immediately after application of the coating, precipitating the hydroxyethyl cellulose which then acts as an adhesive to bind the contiguous pigment particles to each other and to the base and finally drying the coated paper.

This process, while accomplishing the desired result of providing a relatively high pigment to hinder ratio, has certain inherent disadvantages introduced by the relatively high alkali content of the coating colors. These are (1) the variation in surface pH of the coating due to a lack of uniformity in the neutralization of the alkali, thereby causing uneven printing properties; (2) degradation of the surface fibers of the base stock by the alkali with a resulting loss in brightness; and (3) the diificulty of handling and of disposing of waste color.

Now in accordance With the present invention there has been discovered a process for preparing a coated paper using a water-soluble cellulose derivative as a binder for the coating color, thereby obviating the alkali necessary in the process of Erickson. It has unexpectedly been found that the increased adhesive strength Erickson obtained by the use of a Water-insoluble but alkali-soluble cellulose derivative which was precipitated by neutralization of the alkali may be obtained, in the case of a watersoluble cellulose derivative, by coagulating the cellulose derivative with a setting agent. The setting agents which are used to coagulate the cellulose derivative are electrolytes whose constituent ions have a strong affinity' for water molecules. These setting agents are described in detail infra. I

In carrying out the invention a dispersion of a coating pigment in an aqueous solution of a gellable, water-soluble cellulose derivative is prepared. This coating color is applied to a fibrous cellulosic web by any suitable coating device. The coated surface is then contacted with a setting agent which coagulates the adhesive in the coating to form a film of contiguous pigment particles bound together by the cellulose derivative. The excess setting agent is squeezed out and the coated sheet is then dried by any of the means known to the art.

Another variation of this process, called the reverse coating process, comprises impregnating the cellulosic web with an aqueous solution of setting agent forthe cellulose derivative, preferably drying the impregnated paper, although this step is not absolutely necessary, cover ing a face of the paper with a continuous coating of pigment dispersed in an aqueous solution of a cellulose derivative, and finally drying the coated paper. Thus, by means of the reverse coating process the steps of dipping the coated paper in the setting agent followed by squeezing the coated sheet are eliminated. This simplified process enables the manufacturer to make use of existing coating machines, which are not designed for the dipping and squeezing steps, without modification.

Whichever process is used, there results a coated paper of the type having a base of cellulosic fibers and a printing surface consistingessentially of a film of contiguous pigment particles interspersed in binder by means of which the pigment is retained on the base.

The coated papers prepared according to this invention have coatings which are much stronger and more resistant to picking than those coatings prepared without the use of a setting agent. At equal concentrations of adhesive, the coated papers prepared according to this invention have pick resistance values from 2 to 5 times greater than those observed in coatings prepared using the prior art Examples 1-27, inclusive To an aqueous solution of the sodium salt of a watersoluble carboxymethylcellulose was added clay in small portions with vigorous agitation. After the clay was added, the stirring was continued until the color was smooth. Additional water was then added to the color to give the desired amount of solids. The amount of sodium carboxymethylcellulose in the initial solution, the amount of sodium carboxymethylcellulose (based on the clay) in the resulting color and the percent solids of the resulting color are set forth in Table I. This color was applied to handsheets of Litho No. 5 raw stock at a coat weight of 11-13 lb. per ream (24 x 36/500) using a Martinson laboratory coater. After application of the coating to the paper, the coated surface of the sheet was brought into contact with a solution of setting agent. The sheets were passed through squeeze rolls at a nip pressure of 20 lb. per linear inch and were dried on an electric hot plate at 200 F. The number of carboxymethyl groups per anhydroglucose unit, i. e., the degree of substitution of the adhesive, the nature of the setting agent and the Pick Resistance (Speed Ranger Units) ttittcstsstassLenaLsiizssLt be number of inch and were dried Color Surface pH The sheets were ,passed :through squeeze rolls at of the coating to the paper, the coated surface of the sheet was brought into contact with a solution of setting Coating-Color sno Viscosity (percent) mmmwmmmmmmmwwmwwmmwmwwwwmmwmm SEC Solution Percent Clay TABLE II Degree 0! Percent substi' SECin' Coating Color 'Clay+ GMC 1 1 44 e itmwmmmmmmmmwmm After application 0M0 1 (onclay) (percent) Percent Degree of Sub- OMCin stitution Solution Percent 55556 6566 6666 2 55M55558 swb oowco oocoaowwwfifiwwmmma uomuuouocoouuooucouununuu Examples 28-:56, inclusive TABLE I.-- SODIUM OAKBOXEMETH-YBCELIJULOSE (CMC) properties of the resulting paper are set forth in the following table:

I Hercules Hi-Shear wiscometer at 390 secr shear.

b Aimiried before setting.

A coating color was prepared as in Examples 1-27, inclusive, using the sodium salt of a water-soluble sulfoethylcellulose in place of sodium carboxymethylcellulose. This color was applied to handsheets of Litho No. 5 raw stock at a coat weight of I l-13'1b. per ream (24 x 36/500) using a Martinson laboratory \coater.

1 Hercules Hl-Shearvlscometer at 390 secs" shear. h Ail-dried before setting.

Examples 57-64, inclusive I of setting agent. The sheets which had been dipped in the setting solution were passed through squeeze rolls at a nip pressure of 20 lb. per linear inch and were dried on an electric hot plate at 200 F. The number of sulfate A coating color was prepared as in Examples 1-'-27 only using the sodium salt of a water-soluble carboxymethyl hydroxyethyl cellulose as the adhesive instead of sodium carboxymethylcellulose. This color was applied groulfs P anhydroglufose unit, the degree of to handsheets of Litho Na 5 raw stock at a coat Weight substitution of the adhesive, the concentration of sodium of 11-13 lb, per a (24 X 36/500) using a Martinson cellulose sulfate in the original solution, the nature of laboratory coater. After application of the coating to the setting agent and the properties of the resulting paper' the paper, the coated surface of the sheet was brought are set forth in the following table:

TABLE IV.SODIUM OELLULOSE SULFATE (SOS) Coating Color Pick RelDeSgree Percent sistance Example of ub- SOS in Setting Agent Sui-lace (Speed stitntion Solution Percent Clay+ Color pH Ranger SOS SOS Viscosity I Units) (on clay) (percent) (cps.)

0. 33 7 7. 5 50 2, 470 none 5. -5. 2. 0 0. 33 7 7. 5 50 2, 780 20% MgClg 6. 0-5. 5 5. 5 0. 33 7 7. 5 50 2, 470 20% MgClz 5. 5- 6. 0 6. 0 0. 33 7 7.5 50 2, 470 25% NaHrPO4 M- 4. 5-5.0 5. 5 0. 33 7 7. 5 50 2, 470 20% C3012 5. 5-6.0 5. 0 0.33 10 7. 5 50 2, 150 20% No.01 5. 0-5. 5 4. 5 0. 33 10 7. 5 50 3, 160 NH: vapor 4. 0-5. 0 4. 0

I Hercules Hi-Shear viscometer at 390 seeshear. Air-dried before setting. Sheets exposed to vapor from boiling concentrated N HrOH for 10 to min.

1nto contact With a solution of setting agent. The sheets Examples 72-80, mcluszve were passed through squeeze rolls at a nip pressure of lb. per linear inch and were dried on' an electric hot plate at 200 F. The number of carboxymethyl u and hydroxyethyl groups per anhydroglucose unit, i. e., the degree of substitution of the adhesive, the concentration; of sodium carboxyrnethyl hydroxyethyl cellulose in the original solution, the nature of the setting agent and the A coating color was prepared as in Examples 1-27, inelusive, using a water-soluble hydroxyethyl cellulose as the coating adhesive instead of the sodium salt of a watersoluble carboxymethylcellulose. The concentration of hydroxyethyl cellulose in the initial solution used to prepare the colors together with the total solids of the resulting colors are shown in Table V. The color so prepared properties of the resulting paper are set forth in Table III. was applied to handsheets of Litho ND 5 MW Stock at a A small amount of NaOH was added to the initial coat weight of 11-13 lb per r am (24 x 36/500) using solutions in some of the examples to reduce the viscosity Martinson laboratory coater. After application of the 0f the COIOI'S. The amount 0f NaOH in the initial SOlllgoating to the, paper, ,the coated surface of the sheet was 110118 and in the colors Produced therefrom is shown in brought into contact with a solution of setting agent. The the following table: sheets were passed through squeeze rolls at a nip pressure TABLE III.SODIUM CARBOXYMETHYL HYDROXYETHYL CELLULOSE (CMHEC) Degree of Coating Color Substitution Percent Percent Pick CMHEO NaOH I Surface Resistance Example in in Setting Agent pH (Speed Carboxy- Hydroxy- Solution Solution Percent Clay+ Color Ranger methyl ethyl CMHEC CMHEC Percent Viscosity Units) (on clay) (percent) N a 0131 (cps) 0. 32 0. 26 7 7. 5 5, 070 none 6. 0-6. 5 3. 0 0. 32 0. 26 7' 7. 5 50 5, 070 25% NuH2PO4- 4. 0-5. 0 4. 5 0. 32 0. 26 7 7. 5 50 5. 0-5. 5 5. 5 0. 32 0. 26 7 7. 5 50 5. 5-6.0 4. 0 0.43 0. 41 I 7 7. 5 50 5.0-5. 5 1. 0 0.43 0. 41 7 7. 5 50 4. 05. 0 5. 5 0. 43 0. 41 7 7. 5 50 3, 250 20% MgClz 4.0-5. 0 4. 0 0. 43 0.41 7 7. 5 5O 3, 250 20% OaCh b 4.0-5.0 3. 5

' Hercules Hi-Sheer viscometer at 390 seer sheer. b Air-dried before setting.

Examples -71, inclusive of 20 lb. per linear inch and were dried on an electric hot A coating c 01m was prepared as in Examples plate at 200 F. The number of hydroxyethyl cellulose and Comalmng 50% solids Whlch consisted of parts stitution of the adhesive, the concentration of hydroxyet-hy-l of sodmm :enulose Sulfate per 100 parts of clay This cellulose in the original solution the natureof the setting color was applied to handsheets of Litho No.5 raw stock agent and the properties of g resulting paper are Set at a coat weight of 1l-13 lb. per ream (24 x 36/500) form inTable using a Martinson laboratory coater- After pp n A small amount of NaOH was added to the initial soluf the coating to the p p the coated rf f t t-ions i some of the examples to reduce the viscosity of sheet was brought into contact with a solution or vapor the colors. The amount of NaOH in the initial solutions groups per :anhydrogluoose unit, i. e., the degree of sub-- and in the colors produced therefrom is shown in the followingtable:

cellulose succinate, etc. Those cellulose derivatives which may have :treeacid igroupssuch. as cellulose. sulfate, sulfo- TABLE V.HYDROXYETHYL 'OELLUBOSE (EEO) P Coating Color Pl k R in De ree ercent Percent cs Example of S ub- HEC NaOH Setting Agent Surface snce (Speed stitutlon in in Percent Clay+ Percent Color pH Ranger Solution Solution EEC NaOH Viscosity Units) (on clay) (percent) D 1. 14 8 1 7. 0. 4 1, 755 none 6. 5-7. 0 1.0 1. 14 8 1 7. 5 50 0. 4 1, 755 20% 021011 6. 0 3. 0 1.14 8 l 7. 5 -50 0. 4 1,755 2 0 6. 0-6. 5 2. 0 l. 14 8 l 7. '5 '60 0.4 1, 755 20% AMSOO: 5.0-5. 5 2. 0 1.14 8 1 7. 5 50 0.4- 1,755 20% N 6. 0-6. 5 2.0 1. 67 0 7. 5 50 0 2, 340 110110 5. 0-5. 5 l. 0 1. 67 10 0 7. 5 50- 0 2, 340 25% NaH'iPO4.-.. 5. 0-5. 5 3.0 1. 67 10 0 7. 5 50 0 2, 340 03012 5. 0-5. 5 3. 5 1.07 10 "0 7.5 50 0 2, 340 20% Al;(SO4)i.. 5. 0-5. 5 2. 5

I Hercules Hi-Sheur viscometer at 390 seer shear.

Alr-drladbet'ore setting.

The pick resistance referred to in the examples was 10btained by means of a Hercules print tester using the method described in The "HerculesPrint Tester" by E51. Barber and I. W. Davisin Tappi,-vol. 3'4, page-433 (October 1951). The higherthe speed ranger number the greater is the pick resistance or the bonding strength of the adhesive.

Any gellable water-soluble cellulose derivative may be used as the binder in preparing the coated papers according to the process of the instant invention. By watersoluble is meant that the cellulose derivative at a 5% by weight concentration is completely dispersible in Water. A small amount of alkali, i. e., less than about 1% by weight based on the total weight of the coating'color, may be added if higher concentrations of binder or lower viscosities in the resulting coating color'are desired.

Cellulose itself is not water-soluble despite the large number of hydroxyl groups contained in the molecule. This is due to the fact that the cellulose chains fi-t so well against one another that linking or adjoining'chains by hydrogen bonding occurs. Moreover, the cellulose molecule is rigid enough to prevent a relatively short segment from liftingofi without disturbing 'the neighboring portion of the chain. Waterdoes not form a stable enough complex with the hydroxyl groups to destroythe' h-ydrogen bonding. The insertion of substituent groups into the cellulose chain pushes apart the cellulose molecules, rendering the hydroxyl radicals availablefor hydration. To get smooth solutions, enough substituentgroups have to be introduced throughout the whole molecule totinsure complete separation of the less substituted portions of the chains by water. If too many substitue'nt groups are introduced, however, the number of hyduoxyl groups available for hydration is greatly reduced, and runlessqthe substituent group itselfis capable of hydration, the product is incompletely soluble or only swelled by water. If thc substituent group enters the cellulose molecule in a uniform manner along the cellulose chain, it will be more effective in separating the cellulose molecules than if :it were to be randomly distributed along the chain. .Thus, water solubility can be obtained at lower degrees of substitution when a fairly uniform distribution of 'substituent radicals is obtained. The manner of substitution, i. e., the degree of randomness, is determined by the method of manufacturing the substituted cellulose. Thus, the water solubility of cellulose is determined by the nature of the substituent group, the method of manufacture andthe degree of substitution, -i. e., the average number ofsubstituent groups per anhydroglucose unit. Examples of watersoluble cellulose derivatives are the *alkyl others, such as ethyl cellulose; hydroxyalkyl ethers', such ashydroxyethyl cellulose; sulfoalkyl others, such as sulfoethyl cellulose; carboxyalkyl others, such as carboxymethylcellulose; car-- boxyalkyl hydroxyalkyl ethers, such as-carboxymethyl hydroxyethyl cellulose; cellulose sulfate *and cellulosehzilfesters ofdibasic organic acids, such as cellulose phthalate,

valkyl cellulose, carboxyalkyl cellulose, carboxyalkyl hydroxyalkyl cellulose, and .cellulose half-esters of dibasic organic acids, are used in the form of their water-soluble salts, such astheir sodium, potassium, ammonium, etc., salts. Byth'e terms cellulose sulfate," sulfoalkyl cellulose, -canboxy-alkyl cellulose, carboxyalkyl hydroxyalkyl cellulose, cellulose phth-alate,

n is

cellulose succinatej" etc, as used throughout the specification and claims, is meant the salts of the particular cellulose derivative which possess the requisite solubility characteristics specified above. Examples of operable ranges of substitution in 'terms of the average number of substituent groups per arthydroglucose unit for particular cellulose derivatives are: .hydroxyethyl cellulose, about 1.1 to about 1.7; sodium carboxymethylcellulose, about 0.5 to about 1.3; sodium sulfoethyl cellulose, about 0.3 to about 0.6; sodium cellulose sulfate, about 0.2 to about 1.5; and sodium car'boxymethyl hydroxyethyl cellulose, about 0.3 to about 0.7 .carboxymethyl groups and about 0.2 to about 0.6 hydroxyethy-l groups. It is understood, however, that'thelimitation of substitution for any particular cellulose derivative will vary somewhat with the method of manufacture of the cellulose derivatives. The operable upper limit of substitution for any particular cellulose derivative will vary with the method-of manufacture of the cellulose derivative, with the nature of the setting agent employed, and with the concentration of setting agent used. l he preparation -of 'gellable water-soluble cellulose derivatives will be within theknowledge of those skilled in the art, and it is to be understood that the binder contemplatedherein includes any or all of these derivatives.

The pigment material whichis utilized in the coating color "comprises one of the paper coating fillers such as, for example, a.pulverizecl clay or the like. For higher quality or special types of paper, there may be substituted therefor other known pigment materials such as, for example, titanium dioxide, satin white or other coating pigments-alone or preferably with a clay base. The modification of the coating color using; these materials willbe within the knowledge of 'those skilled in the art, and itis-to-be understoodthatthe'pigment material contemplated herein. includes any or all of these materials.

The amount of binder in the coating color is maintained between 3% and about 15% based on the weight of the pigment and preferably between 6% and 8%. In general, the binder content will depend upon the grade and the end use of the paperbeingprepared.

For optimum results in the coating :of paper it is ,preferred to prepare a coating color havinga total solids composition which is relatively high,-thus providing good surface coating quality and economic operation. A preferred range of total solids for the coating color is between about 30% 'and '65%solids'with an optimum value at about 40% to 55%.

Any setting agent for'the particular water-soluble cellulose derivative employed may be used. in accordance with this invention. The ability of the setting agent to coagulate the cellulose derivative is directly dependent upon the fundamental nature of its constituent ions and in particular upon its affinity for water molecules. The ions of the setting agent are thought to compete with the particles of the cellulose derivative for the available water. The highly polar ions attract the dipolar water molecules more strongly than do the relatively nonpolar cellulose derivative particles, thereby dehydrating the cellulose derivative causing it to coagulate. The efilcacy of an ion in coagulating the cellulose derivative is therefore attributed to its tendency to become hydrated. Among the setting agents which may be used to coagulate the watersoluble cellulose derivatives are the following: the watersoluble halides and nitrates of the alkali metals, the alkaline earth metals, magnesium and zinc; the monoand di-alkali metal phosphates, etc. The following have also been used as setting agents; the sulfates of the alkali metals and of aluminum, magnesium and zinc; ammonia vapor; ammonium chloride, ammonium sulfate, etc. The efiicacy of a particular setting agent varies somewhat with the nature of the cellulose derivative. In general, the preferred setting agents are monoand di-sodium phosphate, magnesium chloride, calcium chloride, zinc nitrate and sodium chloride.

The setting agent is applied to the paper in the form of an aqueous solution preferably of about 10% to about 30% concentration, except when ammonia vapor is used. Although the concentration of the solution is not critical, it must be high enough to coagulate the cellulose derivative. In case the reverse coating process is used, it may be desired to incorporate a wetting agent in the aqueous solution to facilitate impregnation of the base stock.

Any suitable coating machine known to those skilled in the art may be used. Thus, the machine may be a shaft coater, a roll coater, a knife coater, an air brush coater, a gravure or letter press-type, etc.

The setting agent may be heated to 150 to 200 F. to speed up the reaction, but this step is not necessary.

The coated paper may be dried by any suitable means, but it is preferred to dry the paper in contact with a drum drier or a series of paper machine drier rolls.. This drying under tension minimizes cockle from shrinkage. In the case of cellulose derivatives which are very highly water-soluble, it is desirable to subject the coated paper.

to a preliminary drying before contacting the coated paper with the setting agent. This preliminary drying prevents the coating from being squeezed off by the roller and the subsequent treatment with the setting agent coagulates the binder to give a coating of improved bonding strength.

Papers prepared according to the process of this invention have good printing properties and give glossy prints which dry rapidly. The coatings laid down according to this process have an exceptionally high pick resistance, evidencing exceptionally good bonding between the coating and the paper base.-

What I claim and desire to protect by Letters Patent 1. The process for preparing a coated paper of the type having a base of cellulosic fibers and a printing surface consisting essentially of a film of contiguous pigment particles interspersed in binder by means of which the pigment is retained on the base, comprising applying to the surface of a web of cellulosic fibers a coating color consisting essentially of a pigment dispersed in an aqueous solution of a gellable water-soluble sodium sulfoethyl cellulose as the binder, said coating color having from about 30% to about 65 total solids and having said binder present in the amount of between about 5% and about 15% based on the weight of the pigment, and after application of said coating color coagulating said watersoluble sodium sulfoethyl cellulose by contacting said coating color with a water solution of a setting agent selected from the group consisting of the monoand di-- alkali metal phosphates and the water-soluble halides and nitrates of the alkali metals, the alkaline earth metals, magnesium, and zinc, squeezing off the excess solution, and then drying the paper.

2. The process for preparing a coated paper of the type having a base of cellulosic fibers and a printing surface consisting essentially of a film of contiguous'pigment particles interspersed in binder by means of which the pigment is retained on the base, comprising applying to the surface of a Web of cellulosic fibers a coating color consisting essentially of a pigment dispersed in an aqueous solution of a gellable water-soluble sodium carboxymethylcellulose as the binder, said coating color having from about 30% to about total solids and having said binder present in the amount of between about 5% and about 15% based on the weight of the pigment, and after application of said coating color coagulating said water-soluble sodium carboxymethylcellulose by contacting said coating color with a water solution of a setting agent selected from the group consisting of the monoand di-alkali metal phosphates and the water-soluble halides and nitrates of the alkali metals, the alkaline earth metals, magnesium, and zinc, squeezing off the excess solution, and then drying the paper.

3. The process for preparing a coated paper of the type having a base of cellulosic fibers and a printing surface consisting essentially of a film of contiguous pigment particles interspersed in binder by means of which the pigment is retained on the base, comprising applying to the surface of a web of cellulosic fibers a coating color consisting essentially of a pigment dispersed in an aqueous solution of a gellable water-soluble sodium carboxymethyl hydroxyethyl cellulose as the binder, said coating color having from about 30% to about 65% total solids and having said binder present in the amount of between about 5% and about 15% based on the weight of the pigment, and after application of said coating color coagulating said water-soluble sodium carboxymethyl hydroxyethyl cellulose by contacting said coating color with a water solution of a setting agent selected from the group consisting of the monoand di-alkali metal phosphates and the Water-soluble halides and nitrates of the alkali metals, the alkaline earth metals, magnesium, and zinc, squeezing off the excess solution, and then drying the paper.

4. The process for preparing a coated paper of the" type having a base of cellulosic fibers and a printing sur* face consisting essentially of a film of contiguous pigment particles interspersed in binder by means of which the pigment is retained on the base, comprising applying to the surface of a web of cellulosic fibers a coating color consisting essentially of a pigment dispersed in an aqueous solution of a gellable water-soluble hydroxyethyl cellulose as the binder, said coating color having from about 30% to about 65% total solids and having said binder present in the amount of between about 5% and about 15 based on the weight of the pigment, and after application of said coating color coagulating'said water-soluble hydroxyethyl cellulose by contacting said coating color with a water solution of a setting agent selected from the group consisting of the monoand di-alkali metal phosphates and the water-soluble halides and nitrates of the alkali metals, the alkaline earth metals, magnesium, and zinc, squeezing off the excess solution, and then drying the paper.

5. The process for preparing a coated paper of the type having a base of cellulosic fibers and a printing surface consisting essentially of a film of contiguous pigment particles interspersed in binder by means of which the pigment is retained on the base, comprising applying to the surface of a web of cellulosic fibers a coating color consisting essentially of a pigment dispersed in an aqueous solution of a gellable water-soluble cellulose derivative as the binder, said coating color having from about 30% to about 65% total solids and having said binder present in the amount of betweeniabout and about based on the weight of the pigment, and after application of said coating color coagulating said water-soluble cellulose derivative by contacting said coating color with a water solution of an alkali metal acid phosphate, squeezing off the excess solution, and then drying the paper.

6. The process for preparing a coated paper of the type having a base of cellulosic fibers and a printing surface consisting essentially of a film of contiguous pigment particles interspersed in binder by means of which the pigment is retained on the base, comprising applying tothe surface of a web of cellulose fibers a coating consisting essentially of a pigment dispersed in an aqueous solution of a gellable water-soluble cellulose derivative as the binder, said Coating color having from about to about 65% total solids and having said binder present in the amount of between about 5% and about 15% based on the Weight of the pigment, and after application of said coating coagulating said water-soluble cellulose derivative by contacting said coating with a water solution of an alkaline earth metal halide, squeezing off the excess solution, and then drying the aper.

7. The process for preparing a coated paper of the, type having a base of cellulosicy'fibers and a printing surface consisting essentially of a film of contiguous pigment particle's interspersed in binder, by means of which the pigment is retained on the base, comprising applying to the surface of a web of cellulosic fibers a coating consisting essentially of a pigment dispersed in an aqueous solution of a gellable water soluble cellulose derivative as the binder, said coating color having from about 30% to about 65% total solids and having said binder present in the amount of between about 5% and about 15% based on the weight of the pigment, and after application of said coating coagulating said water-soluble cellulose derivative by contacting said coating with a water solution of an alkaline earth metal nitrate, squeezing off the excess solution, and then drying the paper.

8. The process for preparing a coated paper of 'the surface of a web of cellulosic fibers a coating color consisting essentially of a pigment dispersed in an aqueous solution of a gellable water-soluble cellulose derivative as the binder, said coating color having from about to about total solids and having said binder present in the form of between about 5% and about 15% based on the weight of the pigment, and after application of said coating color coagulating said water-soluble cellulose derivative by contacting said coating color with a water 12 solution of an alkali metal halide,'squeezing off the excess solution and then drying thepaper.

9. In the process for-preparing a coated paper of the type having a base of cellulosic fibers and a printing surface consisting essentially of a film of contiguous pigment particles interspersed in binder by means of which the pigment is retained on the base comprising applying to the surface of a web of cellulosic fibers a coating color consisting essentially of a pigment dispersed in aqueous solution of a gellable, water-soluble cellulose derivative as the binder, said coating color having from about 30% to about 65% total solids and having said binder present in the amount of between about 5% and about 15% based on the weight of the pigment, and drying the paper, the improvement which comprises coagulating said Watersoluble cellulose derivative before drying the paper by contacting said coating color with a setting agent selected from the group consisting of the monoand iii-alkali metal phosphates and the water-soluble halides and nitrates of the alkali metals, the alkaline earth metals, magnesium, and zinc.

10. The process for preparing a coated paper of the type having a base of cellulosic fibers and a printing surface consisting essentially of afilm of contiguous pigment particles interspersed in binder by means of which the pigment is retained on the base, comprising applying to the surface of a Web of cellulosic fibers a coating color consisting essentially of a pigment dispersed in an aqueous solution of a gellable Water-soluble cellulose derivative as the binder, said coating color having from about 30% to about 65% total solids and having said binder present in the amount of between about 5% and about 15% based 1 on the weight of the pigment, and after application of said coating color coagulating said water-soluble cellulose derivative by contacting said coating color with a Water solution of a setting agent selected from the group consisting of the monoand di-alkali metal phosphates and i the water-soluble halides and nitrates of the alkali metals,

the alkaline earth metals, magnesium, and zinc, squeezing off the excess solution, and then drying the paper.

References Cited in the file of this patent UNITED STATES PATENTS 

1. THE PROCESS FOR PREPARING A COATED PAPER OF THE TYPE HAVING A BASE OF CELLULOSIC FIBERS AND A PRINTING SURFACE CONSISTING ESSENTIALLY OF A FILM OF CONTIGUOUS PIGMENT PARTICLES INTERSPERSED IN BINDER BY MEANS OF WHICH THE PIGMENT IS RETAINED ON THE BASE, COMPRISING APPLYING TO THE SURFACE OF A WEB OF CELLULOSIC FIBERS A COATING COLOR CONSISTING ESSENTIALLY OF A PIGMENT DISPERSED IN AN AQUEOUS SOLUTION OF A GELLABLE WATER-SOLUBLE SODIUM SULFOETHYL CELLULOSE AS THE BINDER, SAID COATING COLOR HAVING FROM ABOUT 30% TO ABOUT 65% TOTAL SOLIDS AND HAVING SAID BINDER PRESENT IN THE AMOUNT OF BETWEEN ABOUT 5% AND ABOUT 15% BASED ON THE WEIGHT OF THE PIGMENT, AND AFTER APPLICATION OF SAID COATING COLOR COAGULATING SAID WATERSOLUBLE SODIUM SULFOETHYL CELLULOSE BY CONTACTING SAID COATING COLOR WITH A WATER SOLUTION OF SETTING AGENT SELECTED FROM THE GROUP CONSISTING OF THE MONO- AND DIALKALI METAL PHOSPHATES AND THE WATE-SOLUBLE HALIDES AND NITRATES OF THE ALKALI METALS, THE ALKALINE EARTH METALS, MAGNESIUM, AND ZINC, SQUEEZING OFF THE EXCESS SOLUTION, AND THEN DRYING THE PAPER. 